Amory Blaine is the only child of an alcoholic mother and an absent father. As his mother’s companion, he spends his early childhood traveling and living in hotels. When Beatrice’s alcoholism results in a breakdown, Amory goes to live with an aunt and uncle in Minneapolis, where he resides for nearly two years. These years are encapsulated in the description of a party and first kiss shared with Myra St. Claire, and the pattern of Amory’s subsequent life is established as one of anticipation and disappointment. His fledgling character also emerges, as Amory assumes an aristocratic posture.

Amory is reunited with Beatrice at the family estate in Lake Geneva, Wisconsin, before traveling east to attend prep school at St. Regis’s. After taking his entrance examinations, Amory visits his mother’s friend Monsignor Darcy in New York City. Darcy becomes a mentor and confidant of Amory. At St. Regis’s, where he spends two years from ages fifteen to seventeen, Amory begins badly but eventually distinguishes himself as a star quarterback, actor, and editor of the school paper, though when later he recalls his prep school years he remembers his failures more than his successes.

In 1913 at age seventeen, Amory enters Princeton University. In his freshman year, he lives with Kerry Holiday and Tom D’Invilliers and he begins a friendship with Alec Connage. Amory begins to write poetry and vows to make more of his abilities in his sophomore year. Most concerned with his own accomplishment, Amory is unaffected by outside events such as the beginning of World War I. He achieves success as a writer and actor in the fall of his sophomore year. In Minneapolis between terms, he begins a romance with Isabelle Borgé. At the end of his sophomore year, Amory and his classmates travel to New York City. On the return trip to Princeton, a car accident caused by drunken driving kills Dick Humbird.

Amory ends his relationship with Isabelle, and before his junior year he fails an important mathematics examination. When his father dies, he learns of the family’s fading financial fortunes. He discovers the poetry of Rupert Brooke and begins to publish his own poems. On a drunken outing in New York City, he sees an apparition of a man in a brown suit wearing slippers that curl upward at the toes. Unnerved, Amory is convinced he has seen the devil.

In his last year at Princeton, Amory reads seriously and disdains the certainties of the Victorians. For a brief time, he thinks he is in love with Clara Page, a widowed third cousin who lives in Philadelphia. He has solemn conversations with Burne Holiday, who has renounced the social victories of college to become a socialist and pacifist. Amory leaves Princeton for a post as a second lieutenant in the infantry.

When he is twenty-three and has been discharged from the Army, Amory falls deeply in love with nineteen-year-old Rosalind Connage, Alec’s sister. Amory’s job writing advertising copy pays modestly, however, so, with deep regret on both sides, Rosalind ends their relationship and eventually becomes engaged to a wealthier man. Amory then embarks on a three-week alcoholic binge, during which he quits his job and is beaten up. This spree ends with the passing of Prohibition. In Maryland, Amory meets Eleanor Savage, a literate, sharp-witted, and reckless eighteen-year-old. Their three-week affair ends with Eleanor riding a horse off a cliff, though she jumps to safety.

In Atlantic City with Alec Connage, Amory chooses to sacrifice himself by pretending to detectives that he is with the underage woman Alec brought across the state line in violation of the Mann Act. During this episode, Amory sees an aura of evil that his sacrifice dispels. His family’s finances worsen, and Monsignor Darcy dies. Feeling more on his own than ever, Amory takes realistic stock of his character, deciding that the antidote to his ingrained vanity and selfishness is helping others feel more secure.

Restless and down to his last twenty-four dollars, Amory sets off on a long walk toward Princeton. He is picked up by a limousine, and as Amory talks to the car’s owner, he tries out a number of ideas on the pace of modern life, the barriers to progress, and the advantages of socialism. The rich man turns out to be the father of Jesse Ferrenby, a Princeton classmate who was killed in the war. The novel ends with a disillusioned Amory admitting that he knows himself but nothing more.